"The only thing I walked out of Target with [Sunday] was laundry detergent," said Kristin Brooks, 25, of New York. Brooks, who blogs about fashion at TheKrissBliss.com, found the online selection depleted by 8 a.m., and just a few blouses and dresses left on the racks at her store. Other shoppers reported similar experiences.

By Target's account, the collection—as with all new inventory—was added in a series of rolling site updates in the wee hours. "In this case specifically, pieces of the collection became available after midnight Central time," said spokesman Joshua Thomas.

Web platforms got the updates a little before mobile ones. A landing page for the collection was the last to arrive, after all the items were available for purchase online. "We certainly apologize for any frustration or any confusion," he said.

But some shoppers found that searching Target's site didn't turn up any of the Phillip Lim collection until around 4 a.m. Eastern. "Some people saw the preview site, but said it was slow loading," said Hallie Wilson, who blogs about fashion at corals + cognacs. "Others didn't see anything."

The exception: Twitter users following the #PhillipLimforTarget hashtag.

There, several bloggers posted links before midnight Eastern to a test landing page for the collection on Target—one that included links to some already-shoppable items. (Using one of the test page links tweeted out, I received a confirmation email for my first order—including a tuxedo jacket, trench coat and two dresses—at 11:13 p.m. Eastern on Saturday. The items shipped Monday.)

Links to more individual products quickly followed, letting shoppers who weren't seeing items on Target's site find and buy them. "I started playing with the end of the URL, the product ID number," said Wilson. When she hit on an item through that trial and error, she tweeted the link with the collection hashtag for other shoppers to try.

Lisa Barber, who blogs at PhysicalCanvas.com, took a different approach. When she couldn't see anything other than the collection preview page at Target.com, she started Googling for direct product links to post. "People started asking, 'Have you seen this? Have you seen that?'" she said. "Anything I found, I posted and tagged."

(It's worth noting, neither Wilson nor Barber were shopping themselves—they just wanted others to have a less stressful shopping experience. "It felt like a really cool opportunity to help people out," Barber said.)

For some, such links made a difference between grabbing an item, or not. Chicago resident Eva London, 25, was waiting up for the $35 taupe mini satchel, which resembles full-price Phillip Lim bags that sell for upward of $600. By tracking the hashtag, London—who blogs about fashion at InHerGlam.com—was able to snag one a little before 3 a.m. Central, just before they sold out.

The lesson for shoppers: Social media is increasingly an edge for scoring deals, particularly for in-demand launches and big sales. "The Web shopper used to be a comparison shopper looking for the lowest price," said Jeff Green, an independent retail analyst based in Phoenix. "Now it's about social media and who has the word first."